In recent years, aromatic compounds and heterocyclic compounds having the π conjugated system are used for their luminescence characteristics and electron/hole transport ability characteristics in a variety of electronic devices such as organic electroluminescence devices, cells and semiconductors.
Organic electroluminescence devices can be roughly classified into high molecular devices and low molecular devices. As an adequate degree of ready carrier mobility and appropriate fluorescence emission characteristics are required especially for low molecular devices, it is needed to freely vary the band gaps of derivatives of π conjugated compounds upon their developments. Their film characteristics are also important, and in particular, they are required to form stable amorphous films (see Non-patent Document 1, Non-patent Document 2, Non-patent Document 3, and Patent Document 1).
For cells, it is required to control the oxidation-reduction potential of a compound (see, for example, Non-patent Document 4). Concerning an electrode active material for cells, in particular, it is necessary to control its oxidation-reduction potential below the decomposition voltage of an electrolyte solution. It is, therefore, an important endeavor to control the oxidation-reduction potential.
With respect to semiconductors, π conjugated polymers are widely investigated to achieve bandgap narrowing. However, π conjugated polymers involve a problem in that their structures are hardly controllable because they generally have low solubility in solvents and cannot be handled with ease.
As another method for narrowing the bandgaps of π conjugated systems, there is a method that widens the π conjugated systems two-dimensionally (see Non-patent Document 5 and Non-patent Document 6). These materials are also insoluble in solvents so that they cannot be handled with ease.
Further, general π conjugated polymers can behave as impurity semiconductors by doping. It is, however, difficult to stably prepare p-type and n-type semiconductors with a single material.
As electroconductive polymers, polymers of aniline or aniline derivatives are used widely. In general, these polymers are synthesized by electrolytic polymerization or chemical polymerization and are doped with a Lewis acid or the like to impart electroconductivity. Such an aniline polymer has been reported to show a very high specific electric conductivity when it is formed into a thin film by dispersing it in water or an organic solvent to formulate a varnish and spin-coating the varnish on a substrate or the like (see Patent Document 2).
Aniline polymers are, however, accompanied by a drawback that they are not resistant to oxidation by oxygen in air and depending on the degree of oxidation, their specific electric conductivities may be significantly impaired. Moreover, it has also been pointed out that benzidine, a carcinogenic compound, may mix in as a byproduct upon polymerization (see Non-patent Document 5 and Non-patent Document 7).
Polymers of pyrrole are also known as electroconductive polymers. Like aniline polymers, however, these pyrrole polymers are insoluble and infusible and therefore, they involve a problem that they can be hardly formed into films.
On the other hand, polythiophene compounds generally have low dispersibility or solubility in organic or aqueous solvents, and therefore, can be hardly formed into polymer films, dispersions or solutions. Taking process aspects into consideration, the low dispersibility or solubility poses a serious problem upon their application as electroconductive polymer materials.
As a countermeasure, it is conducted to introduce a hydrocarbon group to the 3-position of a thiophene monomer such that the corresponding polythiophene can be provided with improved solubility in an organic solvent (see Patent Document 3).
Further, Bayer AG has reported a varnish of a water-soluble electroconductive polymer as formulated by subjecting (3,4-ethylenedioxy)thiophene or its derivative to oxidative polymerization while using polystyrenesulfonic acid as a dopant (see Patent Document 4).
Polythione-based electroconductive polymers are, however, accompanied by a problem in that their solid concentrations at which they can be stably dispersed are extremely low, thereby making it difficult to control the thickness of each coating film.
As described above, the conventionally-known electroconductive polymers involve one or more of the various problems for their physical properties upon their formation into electroconductive thin films. There is, accordingly, an outstanding demand for a new material having the potency of solving these problems.
Non-patent Document 1:                Polymer, Vol. 24, p. 748, 1983 (U.K.)        
Non-patent Document 2:                Japanese Journal of Applied Physics, Vol. 25, p. 775, 1986        
Non-patent Document 3:                Applied Physics Letters, Vol. 51, p. 913, 1987 (U.S.A)        
Non-patent Document 4:                Electrochemistry (written in Japanese), Vol. 54, p. 306, 1986        
Non-patent Document 5:                Synthetic Metals, Vol. 69, p. 599-600, 1995 (U.S.A.)        
Non-patent Document 6:                Journal of the American Chemical Society, 117(25), 6791-6792, 1995 (U.S.A.)        
Non-patent Document 7:                Achievement Report on Research and Development of Electroconductive Polymer Materials, 218-251, March, 1989 [Book and Reference Material Library, New Energy and Industrial Technology Development Organization (NEDO)]        
Patent Document 1:                U.S. Pat. No. 4,356,429 A        
Patent Document 2:                U.S. Pat. No. 5,720,903 A        
Patent Document 3:                JP-A 2003-221434        
Patent Document 4:                JP-A 2002-206022        